1. Field of the Invention
The present invention relates to a mobile communication system.
2. Description of the Conventional Art In order to study new technologies related to the 4th generation mobile communications, the 3rd Generation Partnership Project (3GPP) who enacts the technical standards of 3G mobile communication systems has proceeded with studies on the Long Term Evolution/System Architecture Evolution (LTE/SAE) technologies since the end of 2004 as a part of the effort to optimize and enhance the performance of 3GPP technologies.
The SAE led by 3GPP SA WG2 is a study on network technologies for the purpose of determining a network structure together with the LTE work of 3GPP TSG RAN and supporting mobility between heterogeneous networks. In recent years, the SAE has been considered one of the latest important standard issues in 3GPP. It is a work to develop a system supporting various radio access technologies on the basis of 3GPP IP systems, and has been progressed to aim at an optimized packet based system that minimizes a transmission delay with enhanced transmission capability.
A high-level reference model defined by 3GPP SA WG2 includes a non-roaming case and roaming cases having various scenarios, and the detailed description thereof is given in 3GPP standard documents TS 23.401 and TS 23.402. In FIG. 1, there is illustrated a structural diagram of a network in which the model is schematically reconfigured.
FIG. 1 is a structural diagram illustrating an evolved mobile communication network.
One of the distinctive characteristics of the network structure of FIG. 1 is that it is based on a 2-tier model having an eNode B of the Evolved UTRAN and a gateway of the core network. The eNode B has a similar function, although not exactly the same, to the eNode B and RNC of the existing UMTS system, and the gateway has a function similar to the SGSN/GGSN of the existing system.
Another distinctive characteristic is that the control plane and the user plane between the access system and the core network are exchanged with different interfaces. While one lu interface exists between the RNC and the SGSN in the existing UMTS system, two separate interfaces, i.e., S1-MME and S1-U, are used in the Evolved Packet Core (SAE) system since the Mobility Management Entity (MME) 51 taking charge of the processing of a control signal is structured to be separated from the gateway (GW). For the GW, there are two types of gateways, a serving gateway (hereinafter, ‘S-GW’) 52 and a packet data network gateway (hereinafter, ‘PDN-GW’ or ‘P-GW’) 53.
FIG. 2 is a view illustrating a relation between (e)NodeB and Home (e)NodeB.
In the 3rd or 4th generation mobile communication systems, attempts continue to increase their cell capacity in order to support high-capacity and bi-directional services such as multimedia contents, streaming, and the like.
In other words, with the development of communication and widespread multimedia technologies, various high-capacity transmission technologies are required, and accordingly, a method of allocating more frequency resources is used to increase radio capacity, but there is a limit to allocate more frequency resources to a plurality of users with restricted frequency resources.
In order to increase cell capacity, there has been an approach in which high frequency bandwidth is used and the cell diameter is reduced. If a cell having a small cell radius such as a pico cell is applied, it is possible to use a higher bandwidth than the frequency that has been used in the existing cellular system, thereby providing an advantage capable of transmitting more information. However, more base stations should be installed in the same area, thereby having a disadvantage of high investment cost.
In recent years, a femto base station such as Home (e)NodeB 30 has been proposed among the approaches for increasing cell capacity using such a small cell.
Studies on the Home (e)NodeB 30 have been started by 3GPP Home (e)NodeB WG3, and also in recent years, actively proceeded by SA WG.
The (e)NodeB 20 illustrated in FIG. 2 corresponds to a macro base station, and the Home (e)NodeB 30 illustrated FIG. 2 may be a femto base station. This specification will be described based on the terms of 3GPP, and the term (e)NodeB is used when referring to both NodeB and eNodeB. Also, the term Home (e)NodeB is used when referring to both Home NodeB and Home eNodeB.
The interface illustrated in a dotted line denotes the transmission of control signals between the (e)NodeB 20 or Home (e)NodeB 30 and the MME 51. Also, the interface illustrated in a solid line denotes the transmission of data of the user plane.
FIG. 3 is a view illustrating a problem according to the related art.
As illustrated in FIG. 3, if traffic is overloaded or congested at an interface between the (e)NodeB 20 and the S-GW 52, or traffic is overloaded or congested at an interface between the Home (e)NodeB 30 and the S-GW 52, then downlink data to the UE 10 or upload data from the UE 10 is failed to be properly transmitted.
Also, if an interface between the S-GW 52 and the PDN-GW 53 or an interface between the PDN-GW 53 and an Internet Protocol (IP) service network of the mobile communication operator is overloaded or congested, then downlink data to the UE 10 or upload data from the UE 10 is failed to be properly transmitted.
Also, when UE is handed over from a cell being currently serviced to another cell, if the another cell is overloaded, then it will cause a problem of dropping the service of the UE.
In order to solve the foregoing problem, mobile communication operators have changed the S-GW 52 and the PDN-GW 53 to high-capacity devices or have installed more new devices, but it has a disadvantage of requiring very high cost. Furthermore, it has a disadvantage that the amount of transmitted or received data increases exponentially over time, and then overloaded in a short time.
On the other hand, various schemes for optimizing the S-GW 52 and the PDN-GW 53 without installing more mobile communication networks as described above have been presented. For example, there has been presented a technology of making a selected IP traffic offload, namely, SIPTO. It provides a path through nodes of a public network which is not the mobile communication network, i.e., nodes of a fixed network, for the specific IP traffic (for instance, Internet service) of the UE without transmitting or receiving through a path over the mobile communication network.
FIG. 4 is a view illustrating the concept of Selected IP Traffic Offload (SIPTO).
Referring to FIG. 4, a mobile communication system such an Evolved Packet System (EPS) is illustrated in an exemplary manner. The EPC system may include (e)NodeB 20, MME 51, S-GW 52, and P-GW 53. Furthermore, Home (e)NodeB 30 is illustrated therein.
As illustrated in the drawing, the Selected IP Traffic Offload (SIPTO) technology may allow specific IP traffic (for instance, Internet service) of the UE 10 to be offloaded to nodes of a fixed network 70 without passing through nodes within an IP service network 60 of the mobile communication operator.
For example, if the UE 10 is allowed to access the (e)NodeB 20, then the UE 10 can create a session passing through a fixed network 70 such as a public communication network over the (e)NodeB 20 and perform an IP network service through the session. At this time, operator policy and subscription information may be considered.
In order to create the session as described above, a gateway, i.e., a local gateway taking charge of part of the function of GGSN in case of UMTS or a local gateway taking charge of part of the function of P-GW (PDN Gateway) in case of EPS may be provided and used at a position adjacent to the (e)NodeB 20.
This type of local gateway is called a local GGSN or local P-GW. The function of the local GGSN or local P-GW is similar to a GGSN or P-GW.
On the other hand, the SIPTO technology does not use a specific APN. In other words, the offload to IP traffic is supported at the discretion of the core network but does not affect the UE.
As described above, the SIPTO technology has proposed the concept of creating a session to offload data of the UE to a wire network such a public communication network.